"Word nerds will notice an eerie root word in 'mortgage' — 'mort,' or 'death,'" Weller writes. "The term comes from Old French, and Latin before that, to literally mean 'death pledge.'"

That may seem a little severe. After all, the home you've bought is somewhere you're going to live. That's a positive thing, right?

Only if you can afford it.

Quentin Fottrell Marketplace reports that an astounding half of Americans have trouble affording their housing.

According to the "How Housing Matters" survey from nonprofit John D. and Catherine T. MacArthur Foundation and Hart Research Associates, 50% of Americans have made a major sacrifice along the lines of taking on credit card debt or taking a second job in the past three years, just to afford their housing.

Traditionally, experts consider housing costs that require no more than 30% of your household income to be affordable, but Fottrell points out that "15% of American homeowners are living in housing markets where the monthly mortgage payment on a median-priced home requires more than 30% of the monthly median household income — long considered the maximum for rent/mortgage repayments."

The Motley Fool used numbers from the Bureau of Labor Statistics' (BLS) 2013 Consumer Expenditure Survey to calculate the average monthly mortgage payment of Americans, by age, as shown in the graphic below. The numbers include property taxes, various insurance, maintenance, and mortgage interest, all costs that come with holding and paying a mortgage.

You'll notice that the lowest average monthly payment — that of the 75-and-above group — is still $447 a month. If you sort that by percentage of pre-tax income, that's nearly 16% of an average household's income.

The data is also broken down by income level, which you can see on The Motley Fool.

Fool highlights that the numbers are imperfect, but that the overall message still stands: When you commit to a mortgage, the monthly costs of homeownership will probably be more than you expect ... and they'll be that way for decades.

"As a way to describe a 30-year agreement you make with your bank," Weller points out, "the etymology sounds about right."